603, all barrels do a "little serpentine" when fired. That's caused by the harmonic frequencies above its resonant/fundamental one. Their quality has nothing to do with that. It's basic vibration issues well understood by mechanical engineers who use formulas to calculate it for all sorts of reasons; earthquake proofing structures and other things such as smoke stacks (a really big barrel in effect) that's held rigid at one end and free at the other. Check out Modes 1 through 3 in the following and note the serpentine in 3: